Dr. Pär Flodin and colleagues, from the Karolinska Institute in Stockholm, report their findings in the journal Brain Connectivity.

Fibromyalgia syndrome is a common and chronic condition of unknown cause that mostly strikes in middle age, although symptoms can often present earlier. Sufferers typically experience fatigue with long-term pain in several areas of the body, plus tenderness in soft tissues such as the muscles, joints and tendons.

We don't know why, but while men and children can also have it, the vast majority of those diagnosed with fibromyalgia are women. According to the National Institute of Arthritis and Musculoskeletal and Skin Diseases, scientists estimate that fibromyalgia affects 5 million adult Americans.

For their study, the Karolinska researchers compared brain activity in women with and without fibromyalgia. In fibromyalgia patients, they found decreased connectivity between brain areas that process pain and sensorimotor signals. The results showed that the fibromyalgia participants had significantly increased pain sensitivity compared with the control group.

They suggest their findings show reduced brain connectivity may contribute to deficient pain regulation in people with fibromyalgia. The results build on previous studies that have linked abnormal brain activity to poor pain inhibition.

For the study, 22 healthy women and 16 with fibromyalgia underwent functional magnetic resonance imaging (fMRI) brain scans while experiencing different levels of pain by having pressure applied to the thumb.

The day before the scans, the women completed tests to calibrate their pain sensitivity. A computer-controlled pressure stimulator applied pressure to their left thumb, while they rated the sensitivity. Pressure intensities derived from these ratings were then delivered in a random order as the women underwent the brain scans.

The participants had to refrain from taking pain medication and sedatives 48 hours before the assessment of pain and 72 hours before the fMRI scans. Altogether, each received 15 stimuli lasting 2.5 seconds each, at half-minute intervals. The results showed that the fibromyalgia participants had significantly increased pain sensitivity compared with the control group.

When they analyzed the brain scans, the team found differences in brain patterns between the healthy participants and those with fibromyalgia. The fibromyalgia participants showed "functional decoupling" between areas of the brain that process pain signals and other parts, including those that control sensorimotor activity.

The authors suggest this reduction in brain connectivity could impair pain perception.

The co-editor-in-chief of the journal, Dr. Christopher Pawela, an assistant professor at the Medical College of Wisconsin in the US, describes the study as "an important first step" in understanding how the brain affects widespread pain perception, which is a known characteristic of fibromyalgia.